Tunable tracking ferrimagnetic resonator circuits are well known. One example of a ferrimagnetic resonator circuit is a YIG-tuned filter and mixer, as described in U.S. Pat. No. 4,817,200, assigned to the assignee of the present application.
YIG-tuned resonator circuits may include several YIG-tuned resonators connected in series. Each resonator comprises a yttrium-iron-garnet (YIG) sphere suspended between two orthogonal half loop conductors. An RF signal is applied to the input half loop conductor, causing an RF magnetic field in the region of the half loop. In the absence of the YIG sphere, the magnetic field is not coupled to the orthogonal output half loop conductor. The YIG material exhibits ferrimagnetic resonance. In the presence of an external DC magnetic field, the dipoles in the YIG sphere align with the magnetic field, producing a strong magnetization.
Performance of any YIG microcircuit may be optimized by manipulation of the YIG spheres, so that each resonator is tuned to the same frequency. The resonance frequencies should track over the frequency range of interest. The location of each sphere relative to its associated coupling loops, the proximity of the coupling loops to the ground plane, and the uniformity and orientation of the magnetic field all have an effect on the performance of such a microcircuit. Manipulation of these spheres may be accomplished either by tooling external to the microcircuit or by the internal design of the microcircuit. For some YIG microcircuits, where only two degrees of freedom are sufficient, a simple fixed collet arrangement may be used to control a sphere support rod. However, higher performance products require more optimal placement of the spheres, thus requiring greater control over the location of the spheres and therefore more degrees of freedom of movement of the spheres.
In one known design, the microcircuit utilizes four resonators connected in series, each of which includes a YIG sphere secured by a collet on a distal end of a non-magnetic, non-electrically conductive rod. The rod associated with each sphere passes through an O-ring seal in the side of a housing surrounding the circuit. Adjustment of the position of the sphere is accomplished through the use of external tooling which engages the collet on the rod within the housing. One set of tooling is used for adjustment in the X-Y plane, and another set of tooling is used for rotation or Z-axis adjustment. Only one set of tooling can be attached to the collet at any one time, and thus, adjustment in the X-Y plane and rotation or Z-axis adjustments cannot be done at the same time. The tooling is manipulated while watching the location of the sphere through a microscope. However, one drawback with this design is that since visual observation is necessary for proper placement of the sphere, one of the magnets typically must be removed for X-Y plane adjustments, and thus, tuning cannot be performed while the circuit is under test. As a result, the adjustment is an iterative process of testing, removing a magnet, manipulating the spheres, replacing the magnet, and then retesting.
In another known product in which YIG sphere translation is possible, the sphere rod collet is suspended from a housing wall by two O-ring seals. In this apparatus, external tooling is connected directly to the proximal end of the sphere rod, rather than to the collet, for manipulation of the YIG sphere. Movement of the YIG sphere in a direction generally parallel to the housing wall can be produced by pivoting of the sphere rod about the point at which it passes through the housing wall, while movement of the sphere generally perpendicular to the housing wall can be accomplished by pushing or pulling on the sphere rod. In each instance, movement of the sphere is produced by deformation of the O-ring seal. In this design, tuning can be performed while the circuit is under test, without removal of any magnet. Such tuning is accomplished by observing the frequency response of the circuit. While this apparatus eliminates any iterative adjustment process, the magnet must be removed prior to final positioning to apply an epoxy encapsulate to hold the spheres in alignment. The O-ring seals are not able to hold the spheres in alignment by themselves, because of residual stresses due to their resilience. After the magnet is replaced, final adjustments must be made to the system before the epoxy cures to correct for any disruption of the alignment caused by the encapsulation process and by the removal and replacement of the magnet.
In each of the foregoing apparatuses, great care and skill is required to tune the circuit, and the process is time-consuming. Moreover, the danger always exists of accidentally crashing the spheres into the coupling loops surrounding them, causing damage to the spheres or to other portions of the circuit.
It is therefore an object of the present invention to provide improved apparatus for rotation and for manipulation in three axes of the spheres in a ferrimagnetic microcircuit.
It is another object of the present invention to provide apparatus for manipulation of the spheres in a YIG microcircuit which allows tuning under test and which requires no epoxy encapsulate.
It is yet another object of the present invention to provide apparatus for manipulation of spheres in a YIG microcircuit which minimizes the possibility of the spheres contacting the coupling loops or other portions of the microcircuit.
It is yet another further object of the present invention to provide an improved method for tuning of a YIG microcircuit while under test.
It is yet another further object of the present invention to provide external tooling which permits manipulation of the spheres in a YIG microcircuit in a user-friendly manner while under test and which can be engaged or disengaged without disturbing the positions of the spheres.